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IMAGINE OrthoBASE Pro™
Reviewed by: Dr. Thomas Loecherbach, HJW GeoSpatial, Inc. 8407 Edgewater
Drive
Oakland, CA 94621 e-mail:ThomasL@hjw.com Internet: www.hjw.com
(reprinted from PE&RS April 2002)
Vendor Release Date: September 2001
Hardware Minimum Configuration: Intel Pentium II or higher
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Summary Now, with IMAGINE OrthoBASE Pro, a Windows NT- or Windows 2000-based solution is available that smoothly links into the other Windows-based modules. IMAGINE OrthoBASE provides tools for determination of exterior orientation parameters by automatic tie point collection and aerotriangulation (AT) for orthorectification. With the addition of DEM extraction, IMAGINE OrthoBASE Pro provides the missing link between AT and orthorectification by providing DEM data. Both modules require a license for the ERDAS image processing software IMAGINE Advantage. Editing of the DEM data is possible either in IMAGINE Advantage or in Stereo Analyst. While IMAGINE Advantage includes a multitude of image processing tools, IMAGINE OrthoBASE, IMAGINE OrthoBASE Pro, and Stereo Analyst together make up what ERDAS calls their Photogrammetry Product Suite. For a review of IMAGINE OrthoBASE prior to IMAGINE OrthoBASE Pro, see PE&RS 5/2000. For a review of Stereo Analyst, see PE&RS 9/2001. IMAGINE OrthoBASE Pro comes with a 30-day evaluation license, a set of tutorial data, and extensive documentation. As input for DEM extraction, it uses a variety of common image formats and either the AT results generated by IMAGINE OrthoBASE or exterior orientation parameters imported from external sources. It generates DEM data in the form of IMAGINE *.img raster files, TIFF raster files, ESRI Shapefiles, Terramodel TIN (Triangulated Irregular Network) files, or plain ASCII files. DEMs are generated either as individual DEMs per stereo model, or as a mosaicked DEM for the entire block. The software is designed to process large data sets in a GUI-based production environment and provides tools for quality analysis. Features The latter data set consisted of five images of mountainous terrain and was relatively challenging mainly because it contained some heavily forested areas. In both cases, the exterior orientation parameters were known; therefore, no AT had to be performed in IMAGINE OrthoBASE. The evaluation was performed on a Pentium II 266 Mhz PC with 256 MB of memory and running Windows NT 4.0. Operation Before starting the DEM extraction, the user has to set up an IMAGINE OrthoBASE block file containing at least two images. This binary *.blk file contains all necessary project information, such as interior and exterior orientation parameters, coordinate system, map projection and map units, camera data, input image file names and file paths, output DEM file names and file paths, as well as DEM processing parameters. Once the *.blk file has been defined, the images can be attached, and the image pyramid layers for hierarchical processing must be computed. Then, the AT can be performed, or exterior orientation parameters can be imported instead. DEM Setup
Advanced Parameters Under the General tab, the DEM can be output to a different map projection. An optional contour map can be generated in the form of an ESRI Shape file (*.shp) file, and a point status image that shows the quality of point matching can be produced. Under the Image Pair tab (see Figure 1), the stereopairs can be selected. As the default, the system selects all image pairs with a certain user-defined minimum stereo overlap, e.g. 60%.
The Area Selection tab (see Figure 2) provides probably the most important options for advanced use. It allows for the definition of regions for DEM extraction with associated strategy parameters. As with the previous tab, this tab also allows display of the images.
Finally, the Accuracy tab allows the user to specify reference data for a quality evaluation of the DEM (see Figure 4). This reference data can be either the tie points generated during the IMAGINE OrthoBASE AT process, an external DEM, or a set of check points, imported from an ASCII file. The documentation contains a thorough description of the statistical parameters used for accuracy assessment. When the DEM extraction is finished, the strategy settings, processing times, and accuracy parameters can be reviewed in a report file. The quality of each extracted mass point based on the correlation value is stored together with the point coordinates. Installation and Licensing Documentation and Support ERDAS support by e-mail and phone has always been good, and the development team has usually been very responsive to customer needs. ERDAS also offers training classes for ERDAS IMAGINE and for IMAGINE OrthoBASE Pro. Conclusions One particular strength of IMAGINE OrthoBASE Pro is its ability to process large data sets in a well-organized manner. The user does not have to select much more than a directory and a minimum percent of overlap to start the extraction of DEM data from all stereo image pairs in the directory with the minimum overlap. This is unlike some other products, which often require a lot of mouse click operations to trigger a process. Besides the ease of operation for a novice user, the system provides a lot of flexibility for the advanced user. Although the software is clearly aimed at the non-specialist and the GIS user who needs to generate his or her own DEM data, fine-tuning the extraction parameters to obtain optimal results requires some understanding of the image matching process as well as some experience with the software. IMAGINE OrthoBASE Pro runs relatively fast and has minimum requirements for the hardware. Although it is able to generate a variety of output data formats, editing the data requires either *.img format for area editing in ERDAS IMAGINE, or Shapefile format for mass point editing in Stereo Analyst. Stereo Analyst has not been part of this review since it was reviewed for an earlier edition of PE&RS. Editing the data in Stereo Analyst naturally has much higher hardware requirements. The focus of ERDAS IMAGINE has been to provide image analysis tools for photogrammetry, remote sensing, and mapping. Now, the ERDAS Photogrammetry Product Suite, consisting of IMAGINE OrthoBASE Pro and Stereo Analyst, can be linked into ERDAS IMAGINE at a relatively low cost. Today, the cost of a softcopy workstation ranges from roughly $5,000 to $80,000. IMAGINE OrthoBASE Pro can be obtained for the fraction of the cost of a high-end photogrammetric workstation. Some drawbacks of the software include limitations of the editing capabilities. Also, the algorithm could be expanded to include breakline extraction in addition to mass point extraction. Additionally, in low textured areas or forest areas, points may have to be added in Stereo Analyst. Overall, IMAGINE OrthoBASE Pro is a very useful production tool
to provide DEM data. This data can be used as one of the main
layers of any GIS, a prerequisite for orthorectification, or
as input for generating fly-throughs in IMAGINE VirtualGISä.
IMAGINE OrthoBASE Pro provides comprehensive functionality at
a reasonable cost.
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